Turbines

ABSTRACT

To prevent leakage of fluid through a clearance passage defined between a turbine rotor and stator, a duct is formed in the stator from which an annular jet of fluid can be directed into the passage. The jet forms a moving curtain of fluid between rotor and stator. Axially adjacent the duct, a chamber may be formed in the stator, fluid from the curtain being deflected into the chamber and conveyed therefrom to a further duct in order to provide a further moving curtain between rotor and stator. The further moving curtain may be provided in the same clearance passage or in another located downstream therefrom.

United States Patent [7 2] lnventors Robert George Unsworth;

Robert Keith Burton, both of Rugby, England [21 1 Appl. No. 831,963 {22] Filed June 10, 1969 [45] Patented Aug. 3, 1971 [73] Assignee The English Electric Company Limited London, England [32] Priority June 10, 1968, Aug. 12, 1968 [33] Great Britain [31] 27442/68 and 38557/68 (54] TURBINE 4 Claims, 4 Drawing Figs.

[52] US. Cl. 415/112, 415/175.4l5/l3 L, 277/16 [51] Int. Cl ..F0ld 11/00, FOld 5/08 [50] FieldofSear-eh 415/174, 175, 170;416/90, 172, 91, 92, 93;417/109, 110, 117,l12;277/53,16,133,135

[56] References Cited UNITED STATES PATENTS 2,685,429 8/1954 Auyer 230/122 Primary Examiner-Henry F. Raduazo AtrarneysMisegades & Douglas, Keith Misegades and George R. Douglas, Jr.

ABSTRACT: To prevent leakage of fluid through a clearance passage defined between a turbine rotor and stator, a duct is formed in the stator from which an annular jet of fluid can be directed into the passage. The jet forms a moving curtain of fluid between rotor and stator.

Axially adjacent the duct, a chamber may be formed in the stator, fluid from the curtain being deflected into the chamber and conveyed therefrom to a further duct in order to provide a further moving curtain between rotor and stator. The further moving curtain may be provided in the same clearance passage or in another located downstream therefrom.

Patented Aug. 3, 1971 2 Sheets-Sheet 2 xvi ME FIG. 4

TURBINES be employed, for example, in steam turbines. Where a rotor stage of such a turbine is provided with a shroud around the blade tips it is desirable in the interests of efficiency to seal the clearance passage defined between the shroud and the surrounding casing against leakage of steam therethrough from the highpressure side of the rotor stage to the low-pressure, downstream side. Similarly where a stage of such a turbine is provided with an annular stator diaphragm it is desirable to provide a seal between the radially inner periphery thereof, and the surface portion of the rotor surface which the diaphragm surrounds.

One method of providing such seals involves the use of a number of baffles extending radially from the shroud or the rotor toward, respectively, the surrounding casing or the diaphragm. For such a seal to be effective the radial clearances between the ends of the baffles and the surrounding structure must be small, with the danger, during running, of contact occurring therebetween, leading to localized frictional heating and in consequence, distortion of the rotor. Alternative arrangements wherein the baffles are mounted respectively on the surrounding casing or the diaphragm suffer from the same disadvantage.

Where the baffles extend alternately from the rotor and the casing to form a labyrinth-type seal, an additional problem arises in the need for precise axial alignment of the rotor relative to the casing.

According to the invention, a turbine includes a rotor having at least one rotor stage, and a stator having at least one stator stage, there being annular clearance passages defined between the rotor and the stator at each stage, wherein a seal is provided for at least one passage for maintaining a pressure difference between the upstream side of the passage, and the downstream side thereof, the seal including a first circumferentially extending duct formed within the stator and communicating with the passage, and means for feeding a fluid to the first duct at a pressure greater than the pressure obtaining on either side of the passage, the arrangement being such that an annular jet of said fluid is directed from the first duct into the passage to provide therein a moving curtain of fluid which is deflected due to said pressure difference the fluid having sufficient initial velocity that changes of fluid momentum due to the deflection are sufficient to maintain said pressure difference.

Preferably said fluid is directed from the first duct with an axial component of velocity towards the upstream side of said passage.

A circumferentially extending chamber may be formed in the stator, the chamber communicating with said passage at a point axially adjacent said first duct, at least part of the fluid directed from the first duct being deflected into the chamber and removed therefrom via a conduit formed within the stator, fluid thus deflected being fed by the conduit to a second duct for use in a further annularjet, whereby to form a further moving curtain offluid.

The second duct may be located in the same stage as the first duct. Alternatively, in a turbine having a plurality of stages, the second duct may be located in a stage downstream of that containing the first duct.

The invention enables steam turbines, for example, to be designed with a greater running clearance between selected portions of the rotor and the surrounding casing or diaphragms, thus reducing the danger of rotor distortion occurring during operation. Furthermore, during assembly, the axial alignment of the rotor with respect to the surrounding casing need not be as critical as when labyrinth type seals are employed.

Four embodiments of this invention will now be described, by way of example, with reference to the accompanying drawings, of which:

FIG. 1 is a fragmentary sectional view of a rotor stage of a steam turbine in accordance with one embodiment of the invention;

FIG. 2 is a fragmentary sectional view ofa similar portion of a steam turbine to that shown in FIG. 1, in accordance with a second embodiment of the invention;

FIG. 3 is a fragmentary sectional view of a portion of a steam turbine showing two adjacent rotor stages in accordance with a third embodiment of the invention; and

FIG. 4 is a fragmentary sectional view of a rotor and stator stage of a steam turbine in accordance with one embodiment of the invention.

Referring to FIG. 1, there is shown part of a shroud 10 of one stage of a rotor which is rotatably mounted within a turbine casing 11. An annular passage 12 provides a clearance between the shroud 10 and the adjacent portion of the casing 11. The direction of flow of the working steam which drives the rotor is indicated by the arrows 13.

A duct 14 is formed circumferentially in the casing 11 so as to open into the passage 12. The duct 14 is arranged so as to direct a jet into the passage 12 towards the adjacent surface of the shroud 10 with a component in the direction towards the upstream side (that is the high-pressure side) of the rotor stage shown. The duct 14 is fed from an annular reservoir 15 also formed within the casing 11. The annular reservoir 15 is in communication with a suitable source of steam which is at a pressure above that of the high-pressure side of the rotor stage shown. The suitable source of steam may be independent of the steam driving the rotor. Alternatively, steam may be tapped from a point upstream of the turbine nozzle through which steam is fed to the rotor stage shown, the tapped steam being fed to the annular reservoir 15.

In operation of this embodiment of the invention, an annular jet of steam is ejected from the duct 14 to form a moving curtain of steam which flows across the passage 12 and turns back upon itself to flow towards the downstream side (that is the low-pressure side) of the rotor stage shown. The annular jet-is so arranged that the rate of change of momentum of the moving curtain of steam in the direction parallel to the axis of rotation of the rotor is sufficient to support the pressure difference across the shroud 10. Consequently the moving curtain of steam across the passage 12 presents a barrier to the flow of steam through the passage 12 from the high-pressure side to the low-pressure side of the rotor stage shown.

Referring to FIG. 2, in which like parts have been given the same reference numerals as used in the embodiment of FIG. 1, there is illustrated a second embodiment of this invention which differs from that of FIG. 1 in that additional passages are formed in the casing 11 so that the annular jet of steam which issues from the duct 14 is deflected by the shroud 10 into a duct 16 formed circumferentially in the casing 11 on the upstream side of the duct 14. The steam collected by the duct 16 is fed through a number of circumferentially spaced conduits 17 to an annular chamber 18 and ejected through a duct 19 which interconnects the annular chamber 18 with a point in the passage 12 downstream of the duct 14. The pressure of the steam in the annular reservoir 15 is selected so that the annular jet issuing from the duct 19 behaves in much the same manner as the annular jet of the FIG. 1 arrangement.

It should be understood that, for the same conditions of pressure upstream and downstream of the rotor stage shown, the pressure of steam in the annular reservoir 15 may be lower in this embodiment than in that of FIG. 1. This is because the moving curtain of steam issuing from the duct 19 raises the pressure in the space between itself and the moving curtain of steam issuing from duct 14 so that the latter moving curtain need only support a smaller pressure difference than the single moving curtain of steam of the embodiment of FIG. 1.

In operation of this embodiment, the rate of change of momentum of the moving curtain of steam flowing between the ducts l4 and 16 and of the moving curtain of steam issuing from the duct 19 supports the difference in pressure between the upstream and downstream sides of the rotor stage shown so that the two moving curtains of steam present a barrier to the flow ofsteam through the passage 12 from the upstream to the downstream side of the rotor stage shown.

Referring to FIG. 3 in which like parts have been given the same reference numerals as used in the embodiments of FIGS. 1 and 2, there is illustrated a third embodiment showing the shrouds of two adjacent stages of a rotor. The difference between this embodiment and the other two is that once the moving curtain of steam emerging from a duct 14 of one rotor stage is collected in the duct 16 of that rotor stage it is transmitted through the conduits 17 in the downstream direction to the duct 14 of the next rotor stage. This procedure is repeated until the last stage of the system is reached which stage will function as described with reference to FIG. 1.

In operation of this embodiment it will be appreciated that the rate of change of momentum of the moving curtain of steam flowing between a duct 14 and its associated duct 16 supports the pressure difference across that rotor stage. Furthermore it will be understood that the pressure of the steam which is supplied to the duct 14 of the first rotor stage of the system is such as to ensure that the moving curtain issu ing from the duct 14 of the last rotor stage of the system acts as described with reference to FIG. 1.

Referring to FIG. 4, in which like parts have been given the same reference numerals as used in previous Figures, a steam seal of a type already described with reference to FIG. 1 is shown applied to an annular passage 27 defined between a sta tor diaphragm 25 which supports a ring of stator blades 24, and a surface portion 26 ofa rotor 20. An annular reservoir is formed within the diaphragm, a conduit 28 extending radially therefrom and communicating, via one of the stator blades 24 which has a hollow cross section, with a suitable source of pressurized steam as discussed above.

In operation, steam is fed under pressure to the reservoir 15 via the hollow stator blade 24 and the conduit 28. As in the other embodiments described, an annular jet of steam is directed from the reservoir 15 through the duct 14 with an axial component of velocity directed toward the upstream side of the diaphragm 25. The steam forms a moving curtain of fluid in the annular passage 27 in a manner already described, thereby serving to maintain the pressure difference across the diaphragm and presenting a barrier to fluid flow through the passage 27 from the upstream side of the diaphragm to the downstream side thereof.

It will be appreciated that the seals which have been described with reference to FIGS. 2 and 3 of the drawings could also be employed, for example, in the stator stage described with reference to FIG. 4, additional ducting being provided where required by means of further conduits 28 and additional hollow section stator blades 240.

It will also be appreciated that the seals which have been described with reference to FIGS. 1, 2 and 3 could be applied to the annular clearance passage defined between the shrouded rotor and the surrounding casing shown in FIG. 4.

It will be further appreciated that for all applications of the seal herein described, the flowrate of the seal fluid to the reservoir 15 may be so adjusted that the momentum change undergone by the fluid during deflection is just sufficient to support the pressure difference across the members being sealed and thus provide the required barrier to fluid flow therebetween. However, this state of equilibrium is extremely difficult to maintain exactly. Should the pressure difference pressure cylinder, an intermediate pressure cylinder and a ow-pressure cylinder and may be used with advantage on all the stages of the high-pressure cylinder, most of the stages of the intermediate cylinder and the initial stages of the low-pressure cylinder.

We claim:

1. A turbine including a rotor having at least one rotor stage, and a stator having at least one stator stage, the rotor and the stator defining between them an annular clearance passage at each stage, there being provided a seal for at least one passage for maintaining a pressure difference between the upstream and downstream sides thereof, the seal including:

means within the stator which define a first circumferentially extending duct which communicates with the passage; fluid-feeding means connected to the first duct for feeding a fluid thereto at a pressure greater than the pressure obtaining on either side of the passage, the first duct being arranged to direct an annular jet of fluid into the passage to provide therein a moving curtain of fluid which can be deflected owing to the said pressure difference, the said jet having sufficient initial velocity that changes of fluid momentum during deflection of the jet are sufficient to maintain the said pressure difference; further means within the stator which define a circumferentially extending chamber communicating with the passage at a point axially adjacent to the first duct; and

fluid release means comprising a conduit connected to the chamber, such that at least part of the fluid in the said jet can be deflected into the chamber and released therefrom via the said conduit to a second duct for use in a further annular jet, whereby to form a further moving curtain of fluid.

2. A turbine according to claim 1, wherein the first duct is arranged to impart to the said annular jet of fluid an axial component of velocity towards the upstream side of the passage, and the said chamber is disposed upstream ofthe first duct.

3. A turbine according to claim I, wherein the said second duct is disposed in the same stage as the first duct.

4. A turbine according to claim 1, having a plurality of stages, wherein the said second duct is disposed in a stage downstream from that containing the first duct. 

1. A turbine including a rotor having at least one rotor stage, and a stator having at least one stator stage, the rotor and the stator defining between them an annular clearance passage at each stage, there being provided a seal for at least one passage for maintaining a pressure difference between the upstream and downstream sides thereof, the seal including: means within the stator which define a first circumferentially extending duct which communicates with the passage; fluid-feeding means connected to the first duct for feeding a fluid thereto at a pressure greater than the pressure obtaining on either side of the passage, the first duct being arranged to direct an annular jet of fluid into the passage to provide therein a moving curtain of fluid which can be deflected owing to the said pressure difference, the said jet having sufficient initial velocity that changes of fluid momentum during deflection of the jet are sufficient to maintain the said pressure difference; further means within the stator which define a circumferentially extending chamber communicating with the passage at a point axially adjacent to the first duct; and fluid release means comprising a conduit connected to the chamber, such that at least part of the fluid in the said jet can be deflected into the chamber and released therefrom via the said conduit to a second duct for use in a further annular jet, whereby to form a further moving curtain of fluid.
 2. A turbine according to claim 1, wherein the first duct is arranged to impart to the said annular jet of fluid an axial component of velocity towards the upstream side of the passage, and the said chamber is disposed upstream of the first duct.
 3. A turbine according to claim 1, wherein the said second duct is disposed in the same stage as the first duct.
 4. A turbine according to claim 1, having a plurality of stages, whereIn the said second duct is disposed in a stage downstream from that containing the first duct. 